The present invention relates to coating compositions for glass articles. More particularly, this invention relates to improved abrasion resistant coating compositions for glass articles.
In the United States and several other countries, glass vessels which are used for beer, soft drinks, milk and the like are generally returned after use and then reused. During bottling processes, e.g., packaging and transportation, such bottles undergo considerable abrasion damage, such as grazing, scratching, galling, scoring, and similar abrasive action (hereinafter referred to collectively as "scuffing") whereby scuff marks are left on the surfaces of the glass bottles. Scuffing phenomena is aggravated by mechanical grinding due to bottle-to-bottle pressure, mould lines, guide rails, and caustic etching and leaching. Scuff marks lead to bottle fatigue which makes bottles more susceptible to breakage. In addition, scuffing markedly impairs the appearance of the glass bottles and reduces the commodity value of the resulting bottled beverages.
Efforts have been made to provide coating compositions for concealing scuff marks on bottle surfaces.
Copending, commonly assigned U.S. patent application Ser. No. 07/564,927 (Pawar et al.), filed Aug. 8, 1990, discloses an improved coating composition for glass articles, wherein the composition contains from about 70% to about 100% of (A) a composition containing by weight (1) from about 50% to about 75% of an organooxy-chainstopped organopolysilsequioxane containing RSiO.sub.3/2 units and R(R.sup.1 O).sub.3-2n SiO.sub.n units, (2) from about 5 to about 15 percent of tetraorganotitanate, (3) from 10 to about 20 percent of an organotriorganooxysilane, and (4) from 0 to about percent of a carboxylic acid ester, and (B) from 0 to about 30 percent of a volatile diluent.
U.S. Pat. No. 4,985,286 (Kurita et al.) discloses an abrasion-concealing agent for glass containers, comprising (A) a polyorganosiloxane and (B) a volatile polydimethylsiloxane. The composition also contains a curing catalyst which can be tetrabutyltitanate.
U.S. Pat. No. 4,273,834 (Yokokura et al.) discloses a scuff-masking composition for glass vessels, wherein the composition contains an organopolysiloxane terminated with a phenyl group, a methyl group, and an alkoxy group, and a curing catalyst, e.g., tetrabutyltitanate. The ratio of the phenyl, methyl and alkoxy groups to one another is critical to the scuff-masking properties of the coating in Yokokura et al.
Japanese Patent Application Sho 63-117932 discloses a glass bottle scratch concealing agent which consists of (A) an aqueous waxy substance emulsion and (B) a polyorganosiloxane. The composition may further contain a curing catalyst such as tetrabutyltitanate.
Other compositions for concealing graze marks on glass bottles are disclosed, for example, in U.S. Pat. Nos. 4,656,221 (Kurita et al.) and 4,467,068 (Maruyama et al.).
It is desirable to provide a coating composition for glass articles wherein the coating has improved abrasion resistance to scuffing phenomena.
The present invention is based on the discovery that a coating composition containing certain crosslinkers and/or certain base copolymers will have improved abrasion resistance to scuffing phenomena.
The use of methyltrialkoxysilanes and phenyltrialkoxysilanes as crosslinkers is known in the art. The phenyltrialkoxysilanes provide better abrasion resistance than the methyltrialkoxysilanes but the phenyltrialkoxysilanes are disadvantageous in that their production results in the formation of PCBs and benzene as by-products, which is undesirable because these by-products appear to have a deleterious effect on the environment.
It is desirable therefore to provide an alternative crosslinker to the phenyltrialkoxysilanes as well as to the methyltrialkoxysilanes, wherein the alternative crosslinker is at least equivalent to the phenyltrialkoxysilanes in providing good abrasion resistance to scuffing phenomena but which is not as potentially harmful to the environment. It is further desirable to provide a crosslinker which provides superior abrasion resistance than the methyltrialkoxysilanes.
Such crosslinkers are provided in the present invention.